1. Field of the Invention
The present invention relates to a battery module that is composed of a plurality of batteries arranged side by side, and in particular to a power supply device that includes batteries and evens the temperatures of the batteries to be used for electric motors for driving hybrid cars, fuel cars, and electric vehicles.
2. Description of the Related Art
In vehicle power supply devices, a large amount of current is repeatedly charged/discharged. Accordingly, vehicle power supply devices include a plurality of batteries arranged side by side. When vehicles are driven, the batteries generate heat. As a result, the temperatures of batteries will rise. If the batteries store the generated heat, the batteries will deteriorate in performance. For this reason, it is necessary to cool the batteries. In one of methods for cooling batteries, a cooling structure is constructed in such a power supply device, and cooling air is blown toward the cooling structure to cool the batteries. However, it is difficult to evenly cool the batteries. The reason is that a battery near the cooling air inlet is cooled by colder air at a higher flow rate and is likely to be over-cooled, while a battery, which is the furthest away from the cooling air inlet, is cooled at a lower flow rate relative to the battery on the cooling air inlet side and is likely to be poorly cooled so that a temperature difference among between the batteries will arise. For this reason, as the number of batteries increases, it becomes more difficult to evenly cool the batteries, and the temperature difference will increase. In addition, if a cooling gas or fluid with large thermal capacity is used to increase cooling performance, the temperature difference will increase.
If batteries are unevenly cooled, some of the batteries that are poorly cooled may deteriorate faster so that the lives of some batteries may be reduced. In addition, this unevenness will increase as the batteries are used over a long period of time. Accordingly, the charging/discharging capacities of the power supply device will decrease. Also, some of the batteries will be easily overcharged/over-discharged, which in turn accelerates deterioration of some of the batteries. Consequently, such unevenness may cause life reduction of the power supply device as a whole. For this reason, in vehicle power supply devices, the deterioration of some batteries results in a problem with the power supply device as a whole, and reduces the entire performance of the power supply device. If one of the batteries cannot be used, a power supply device cannot be used that is composed of a plurality of batteries serially connected to each other. For the aforementioned reason, although it is also important for vehicle power supply devices to bring batteries lower than a predetermined temperature, it is more important to control the temperatures of the batteries so as to evenly cool the batteries, which are arranged side by side, so that the temperature difference among the batteries is minimized.
Known battery cooling structures for evenly cooling batteries include a device box arranged on the upstream side of an inlet chamber, and a wall surface of the device box facing the inlet chamber being constructed in various shapes. For example, a battery cooling structure has been developed in Japanese Patent Laid-Open Publication No. 2007-250515.
Specifically, in this battery cooling structure, a member with a protruding portion or a recessed portion is provided on the wall surface of the device box facing the inlet chamber so as to deflect cooling air flow away from a battery pack so that cooling air that flows into cooling air paths on the upstream side is reduced and cooling air that flows into cooling air paths on the downstream side is increased thereby evening flow rates of cooling air in a battery module and reducing the temperature difference.
Also, a battery cooling structure has been developed that includes, instead of the air flow deflecting member that deflects a cooling air flow and is provided on the wall surface of the device box, a driven member that can be driven by an electric motor. In this battery cooling structure, the flow rate of cooling air can be adjusted based on a cooling requirement to reduce the temperature difference.
In addition, if the temperatures of the batteries become high, a ventilation fan is provided with a larger amount of power to increase the flow rate of cooling gas.
In these types of cooling structures that change the flowing direction and the flow rate of cooling air, since cooling air paths are not limited, the cooling air can flow either in longitudinal or traverse directions in the cooling air paths.
In the power supply device disclosed in the JP 2007-250515 A, the air flow deflecting member is provided on a part of the device box on the upstream side of the inlet chamber and deflects cooling air flow so as to even the flow rates and reduce temperature unevenness. However, since the air flow deflecting member requires a shaping process or an attachment process, there is a problem in that productivity will be low. In addition, since material, shaping and assembling costs are required, there is a problem in that the production cost will be high. Also, in this power supply device, since cooling air flow is deflected only on the upstream side where the air flow deflecting member is provided, the deflection amount gets smaller toward the downstream side of the inlet chamber. Accordingly, there is a disadvantage in that the effect will be limited that evens the flow rates in the battery module.
For this reason, this battery cooling structure is not suitable for a structure that includes a number of batteries connected to each other. If a number of air flow deflecting members are provided, pressure loss caused by the air flow deflecting members will be increased. In addition to this, it will be very difficult to optimize the arrangement, shape and the like of air flow deflecting members.
Also, in the battery cooling structure that includes, instead of the air flow deflecting member that deflects a cooling air flow and is provided on the wall surface of the device box, a driven member that can be driven by an electric motor so that the flow rate of cooling air can be adjusted based on a cooling requirement to reduce the temperature difference, this battery cooling structure will have the aforementioned problems and disadvantages, and additionally will have a possibility that the flowing direction and the flow rate of the cooling air may not be adjusted in the event of electric motor failure or the like. If the electric motor cannot be properly activated so that the air flow deflecting member is held retracted in the device box, a battery on the upstream of the inlet chamber may be over-cooled so that the output of this battery may be reduced. As a result, there is a problem in that the battery module may be affected as a whole.
In addition, in this cooling structure, since the flow rate is changed based on the battery cooling requirement, there is a disadvantage in that the position and state of a vortex area produced by the air flow deflecting member will change.
It is an object of the present invention to provide a power supply device that can be simply constructed in various types of structures but can reduce the temperature unevenness ΔT in the power supply device, thereby increasing the life and ensuring the performance of the power supply device.